"Skip always has us ready down toward the end of the game," Moustakas said of manager Ned Yost. "That's our job on the bench. Be ready, be prepared for any situation."
Moustakas was so ready he led off the 11th with a 373-foot homer to right field off a changeup from Houston reliever Jerome Williams. Jarrod Dyson added a run with a single, stolen base, sacrifice and fielder's choice.
"I was in the cage hitting a little bit," Moustakas said. "Getting warmed up in case I went in on defense. That's how we go about our business. Make sure we're ready for any situation."
Moustakas slugged the ball high into the night with the roof open at Minute Maid.
"I hit it pretty good," he said. "I got underneath it a little bit. I was kind blowing as it was up in the air, hoping it was going out. I knew I got it pretty good. I didn't know how far it was going to go, but obviously happy it carried out of here."
It was Kansas City's second homer of the game, but only its fourth of the season.
Moustakas, a left-handed hitter, began the day hitting a paltry .100. He didn't start with the Astros throwing lefty Dallas Keuchel at the Royals.
"It was big for anybody to break through, but it was big for Moose to do it," Yost said. "He's been working really, really hard and tirelessly getting after it. He just needed a little luck, just one good at-bat. That was it tonight."
Kansas City drew within one game of .500 at 6-7 and won for the second night in a row on the road, after losing its first five away from home.
"It felt great," Moustakas said of the homer and the victory. "Slow start, or no slow start, it's a big win for us. Anytime you can get a win on the road, it's a big win. We were able to claw it out and pull ahead at the end."
The Kansas City bullpen was simply brilliant, throwing a spotless five innings. Danny Duffy pitched out of trouble in the bottom of the ninth and 10th innings to earn the win. Duffy underwent Tommy John surgery in May 2012 and started five games for the Royals last year. He was called up from Triple-A Omaha Saturday and retired all seven batters he faced that night at Minnesota.
Wednesday night was only his second relief appearance in the Majors.
"That's a role I've never been in before," he said. "There were a couple of good plays made behind me.
"Whatever they tell me to do, I'm going to do. It's a really fun role to be in, when you're going good. I'm trying to keep it where it's at. Fit in wherever I can. I don't mind either way [start or relief]. I'm grateful for the opportunity. It's a lot of satisfaction in just being here. Hopefully, I can stick around."
Aaron Crow, Kelvin Herrera and closer Greg Holland [save No. 5] all threw one inning of relief for the Royals.
"The whole bullpen did a phenomenal job tonight," Yost said. "[Duffy's] what we talked about, having a power arm that could come into a ballgame, especially a tie game like that. Give you an opportunity to battle back and put a run on the board."
Royals starter Jeremy Guthrie went six innings and didn't pitch badly, but gave up a pair of two-run homers, in the third and sixth innings. He allowed six hits -- including the first of Astros' touted rookie George Springer's career -- and threw 103 pitches.
"I was up in the zone for the most part," he said. "I left a lot of changeups and fastballs up. I didn't execute a lot of pitches, but I was able to stay out of trouble for the most part. The home runs, obviously, were what hurt me. Our offense did a great job to pick us and bring us back."
The Royals trailed 4-2 in the seventh when catcher Salvador Perez contributed a two-run, two-out single to tie the game at 4. It was his only hit in a 1-for-6 evening.
"Salvy's been a clutch player for us all year long," Yost said. "He's done a great job with runners in scoring position."
"That's a tough one to swallow there because we felt like we had the right guys that we wanted in each and every spot and we just didn't get it done," Astros manager Bo Porter said.
Kansas City center fielder Lorenzo Cain was pulled from the game after injuring himself trying to beat out an infield grounder leading off the ninth. First-base umpire C.B. Bucknor called him safe, but Houston manager Bo Porter appealed and the replay showed that Cain was out.
"It's a grade one strain of his groin," Yost said. "It's just day to day."